Gibraltar IBAN parsing rules

Examples

    iex>  %IbanEx.Iban{
    ...>    country_code: "GI",
    ...>    check_digits: "75",
    ...>    bank_code: "NWBK",
    ...>    branch_code: nil,
    ...>    national_check: nil,
    ...>    account_number: "000000007099453"
    ...>  }
    ...>  |> IbanEx.Country.GI.to_string()
    "GI 75 NWBK 000000007099453"